Lecture 7 Flashcards
- Where does gas exchange occur (2 structures) during external respiration?
- Where does gas exchange occur (2 structures) during internal respiration?
- external- alveolus and pulmonary capillaries
- internal- systemic capillaries and systemic tissues
What types of physiologic parameters are measured during a blood gas analysis of arterial or venous blood? (5)
- pH
- PO2
- PCO2
- HCO3-
- BE (Base Excess)
which blood gas is best to evaluate lung function
arterial blood gas
what is important about FiO2 when interpreting PaO2?
If giving animal 100% oxygen the PaO2 will increase
if there is an increase in altitude what will happen to PIO2?
decreases PIO2
what is ficks law?
rate of diffusion across a membrane
Regarding ficks law, what do the following symbols stand for
- D
- ∆P
- A
- D – Rate of gas diffusion
- ∆P – Partial pressure difference
- Want to move from high to low pressure
- A – cross-sectional area of surface
Regarding ficks law, what do the following symbols stand for
- S
- X
- MW
- S – Solubility of gas in the fluid
- X – Diffusion Coefficient, distance of diffusion path
- ex. Pneumonia would have an increased distance of diffusion
- MW– Molecular weight of gas
what does this stand for
The rate of gas movement between the alveolus and the blood in the pulmonary capillary EXTERNAL RESPIRATION
what is dalton’s law
Each gas in a mixture of gases exerts its own pressure, as if all other gases were not present
regarding dalton’s law what does everything stand for
- Px= partial pressure of a certain gas
- Fx= fractional concentration of a gas
- Pt= total pressure, sum of all partial pressures
why is dalton’s law important in respiration?
The changes in gas( ie- O2 or CO2) partial pressures from high to low concentration drives the gas into the blood for diffusion to occur.
- How would you calculate PO2 at atmospheric pressure using dalton’s law
Px= Fx x Pt
- FIO2 = 0.21 (inspired air has 21% oxygen)
- PO2 = 0.21 x 760 mmHg = 160 mmHg
as temperature increases what happens to vapor pressure?
increases
how does the partial pressure of water vapor PH20 effect PO2
- During inhalation, air is warmed to body temperature and humidified in the conducting airways.
- The concentration of oxygen and other gases is reduced by the presence of water vapor molecules-
- Increased temperature = increased water vapor = diluted or decreased PO2
Example: 37°C, PH20 = 47 mmHg
PO2 = FIO2 x (PB - PH20 ) = 0.2094 x (760-47) = 149 mm Hg
Example: 38°C, PH20 = 50 mmHg
PO2 = FIO2 x (PB - PH20 ) = 0.209 x (760 - 50) = 148 mmHg
What if body temperature increases a little?
- what will happen to PO2
- what happens with gas exchange?
- P H20 will dilute PO2 (decrease)
- will have dificult time with gas exchange
what is henry’s law
- Content (quantity) of gas dissolved in a liquid,
e. g. oxygen dissolved in plasma
regarding henry’s law what does everything stand for?
Cx = βx Px
- C = Concentration or Content
•Volumes percent = ml gas / 100 ml liquid - β = solubility coefficient
- P = partial pressure in mmHg
Does CO2 diffuse at the same rate as O2?
CO2 diffuses 20 times faster than O2
Why does CO2 diffuses 20 times faster than O2
- solubility coefficient for oxygen is lower than CO2
Oxygen = 0.00364 ml O2 . dl-1 . mmHg-1
CO2 (solubility)= 0.72
How is solubility related to temperature
solubility decreases as temperature increases
What is hyperbaric oxygenation and what is the physiologic principle?
- Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that tissues absorb more O2
- Breathing O2 under increased pressure dissolves more O2 in the blood
What types of problems can be treated with this type of therapy? (7)
- Treatment for patients with anaerobic bacterial infections (tetanus and gangrene)
- Anaerobic bacteria die in the presence of O2
- Used to treat heart disorders,
- CO poisoning,
- cerebral edema,
- bone infections,
- gas emboli
- crush injuries
Compare and contrast the PO2 and PCO2 of alveolar gas, arterial blood, and venous blood
(what are the values for each)
why is there such a low amount of PO2 in venous blood?
oxygen has been transfered to the tissues
Is the total pressure the same or different compared with atmospheric air- PB of PO2 and PCO2 of alveolar gas, venous blood and arterial blood.
the same
Describe the Alveolar ventilation rate and effect on PAO2 and PACO2
PAO2 increases as PACO2 decreases and vice versa
what is the normal alveolar ventilation rate?
4 L/min
during hyperventilation what will happen to…
- PAO2
- PACO2
- PAO2 ↑
- PACO2 ↓
During hypoventilation what will happen to
- PAO2
- PACO2
- PAO2 ↓
- PACO2 ↑
What would cause alveolar hypoventilation? (4 general things)
- Damage to CNS (e.g. drugs, trauma)
- peripheral nerve injury
- damage to pump (e.g. muscle paralysis, trauma to chest, bloated abdomen)
- Lung resisting inflation (e.g. airway obstruction, decreased lung compliance)
What would cause alveolar hyperventilation?
Exercise- Increased metabolic demand for oxygen and increased temperature
Why is it essential to compare PAO2 and PaO2?
- Used to evaluate the lung’s oxygenation function
- Ideal Lung Function: PAO2 = PaO2
- (Oxygen in alveolus and arterioles should be the same)
- How is PAO2 found?
- PaO2?
- PAO2= it is calculated
- PAO2 = PIO2 – [(PACO2 ) / 0.8]
PIO2 = FIO2 (PB – PH2O)
- PAO2 = PIO2 – [(PACO2 ) / 0.8]
PaO2= it is measured
- What equation is this?
- what is R?
- alveolar gas equation
- R = Respiratory exchange ratio of O2 consumption/CO2 production commonly used value for mammals.
* 1 ml of 02 will produce 8/10 ml of Co2 = 0.8 = R
- What is the A-a difference?
- What is the significance of this difference?
- what is the normal?
- Alveolar air - arterial blood regarding PO2
- assess proper oxygen transfer
3.
What is this equation used for?
solving for PAO2
How would you measure PaCO2?
- By measuring ETCO2 using a capnograph
(remember PACO2 should be the same as ETCO2, alveolus concentration should be equal to the arteriole)
How does a capnograph work?
Attach the end to the endotracheal tube which is connected to the anesthesia machine
Your patient is under anesthesia and Has an ETCO2 > 60 mm Hg
- How could you help your patient?
- Ventilate for them, either manually or with a ventilator
- will blow off CO2 and will bring it down to normal 35-45 mm Hg
